Present day sailing vessels are often equipped with hollow masts, made of a light-weight metal or glass fiber. A serious disadvantage encountered with hollow masts is the sound created when halyards slap against the mast, particularly when the sail is furled. The cabin of the sailing vessel will sometimes act as a resonator, irrespective of whether the mast is seated on the deck of the vessel or passes therethrough. At least some of the halyards of a large number of sailing boats fitted with hollow masts pass longitudinally inside the wall of the masts, and are thus not affected by the wind. Movement of the vessel in the water, such as rolling and pitching movements, however, cause the halyards to strike the inner surface of the mast, to cause a hammering sound.
As will be readily understood, the noise created by vibrations set up in the hollow masts of sailing vessels while said vessels are in harbor, is extremely irritating to those living in the close vicinity of the harbor.
Generally the strength and duration of sound-vibrations generated when striking an elongate hollow member will vary in dependence upon inter alia, the material from which the member is made and the shape and size of said member.
Anti-noise devices for the masts of sailing vessels and the like and methods for preventing noise which might be generated when lines are free to slap against mast-like structures are described in U.S. Pat. No. 3,918,383. According to one feature of that invention the anti-noise device is in the form of a corrugated ring encircling the mast and having longitudinal grooves therein to accommodate the halyards or lines which are thereby triangulated and placed under tension.
While an anti-noise device or a method for preventing noise according to U.S. Pat. No. 3,918,383 may prevent halyards or lines from slapping against the outside of a mast, said device and method obviously cannot prevent a halyard or line inside a hollow mast from slapping against the inner surface of the mast. Further said devices and methods cause no or little dampening or attenuation of sound-vibrations in hollow masts once the sound-vibrations have been generated. Finally anti-noise devices and methods for preventing noise according to U.S. Pat. No. 3,918,383 are only applicable to masts of mastlike structures having halyards or lines extending longitudinally therealong. Thus they are normally not useful for dampening sound emitted from or vibrations generated in tubular ventilation ducts.